1. Field of the Invention
The invention relates to a local network operating in the asynchronous transfer mode (ATM), comprising a plurality of stations which are coupled, via network interfaces comprising a coupling device and a control arrangement, to sending and receiving ring lines and which stations are provided for transmitting user cells containing user-oriented information and at least control cells containing signalling information.
2. Discussion of the Related Art
A local network operating in the asynchronous transfer mode (ATM) is known from the publication "Ohne Chips nichts los"--Standard-Chips fur ATM-Systeme sind im Kommen, by Bernd Reder, Elektronik January 1993, pp. 66 to 75. This paper discusses the current development of integrated circuits used in local networks, which networks operate in the asynchronous transfer mode (ATM). Each station is then connected to the ring lines of the local network via network interfaces. Coupling devices (switches) are used in the network interfaces to control the ATM cell stream.
When an asynchronous transfer mode is used in a system, payload, for example, telephone, video or sound signals, is sent in blocks of fixed length through arrangements for digital signal processing. By a block of fixed length is meant a cell which contains a given number of bytes (for example, 53 bytes). Each cell contains a header field having a length of, for example, 5 bytes, and an information field which accommodates the payload and has a length of, for example, 48 bytes. In such a header field are available routing identifications, error recognition data and control data. Routing identifications are meant to be understood as trunk identifiers and link identifiers. The link identifier, also referenced VCI (Virtual Channel Identifier), contains the description of the destination of the cell in the system. To transmit a cell, a virtual channel is made available in response to the virtual channel identifier. As a rule, a VCI is changed each time an exchange is reached. A trunk group of various virtual channels is referenced a virtual path. A virtual path is identified by the trunk identifier. Such a virtual path is called a virtual path identifier (VPI). Cells are assigned to consecutively determined periods of time. The length of such a period of time depends on the clock rate used as a basis of the transfer components. If no payload is available, empty cells i.e. cells without payload, are transmitted in such a period of time. Cells containing payload are referenced payload cells.
How a connection is set up and broken off (signalling) between two or more stations or network interfaces in the local network cannot be learnt from said paper.